The present invention relates to, as first subject matter, a bypass valve of a device through which a fluid medium flows and that has a variable flow resistance, made up of a valve seat and a valve body that cooperates with the valve seat and to which a preloading force is applied in the closing direction, the valve body being movable in the opening direction by a pressure difference in the medium, exceeding a specifiable threshold value, between the inflow side and the outflow side of the bypass valve, a bypass flow path connecting the inflow side and the outflow side of the bypass valve, while bypassing the device, running through the valve seat. As second subject matter, the present application relates to a device having such a bypass valve. The third subject matter of the present application is a filter insert of such a device.
From DE 100 63 283 A1, a sieve filter is known for lines that conduct a fluid medium, in particular for hydraulic pressure lines in internal combustion engines. The sieve filter is substantially made up of a hollow cylindrical basic body having an inlet and an outlet, and of a fine mesh filter element through which the fluid medium flows. When the filter element is clogged, or in the case of a highly viscous fluid medium, the sieve filter has a bypass function. The sieve filter is effectively connected to a spring element, and, together with the spring element, can be placed between two axially spaced counter-surfaces within the pressure line in such a way that the inlet thereof and the spring element lie against the counter-surfaces with a preloading. Here, a basic body of the sieve filter seals a bypass channel that runs past the filter element. The bypass channel can be cleared by axial displacement of the basic body against the force of the spring element, said displacement resulting from an increase in the pressure of the fluid medium.
A disadvantage of this known sieve filter is that in the case of an opening of the bypass channel it lets through completely unfiltered medium. In many applications, this can cause damage or disturbance to downstream components.
From each of EP 1 199 093 A1, U.S. Pat. No. 5,395,518 A, and JP 10-159 530 A, a device is known having an integrated bypass valve, the device being in each case a liquid filter having a filter insert. In these known liquid filters, the filter insert has a sieve element situated in the bypass flow path, the sieve element being fixedly connected to the filter insert and at the same time supporting a spring that loads the valve body with a preloading force acting in the closing direction.
In these known liquid filters, it is regarded as disadvantageous that in the case of blockage both of the filter insert, or of its filter material body, and of the sieve element, there can occur a failure of the liquid supply and thus disturbance or failure of downstream components such as an internal combustion engine, even if the filter bypass valve opens in the intended manner. Moreover, in this case there is the danger that either the filter material body or the sieve element, or both, will be damaged due to the liquid pressure difference, which necessarily increases strongly when there is blockage; in particular, that these elements will be broken through and destroyed. After the occurrence of such damage, the liquid filter no longer functions at all, and dirt particles, and possibly even parts of the filter material body and/or of the sieve element, can move to the outlet of the liquid filter and to downstream components, where they can cause significant damage.
From DE 19 77 428 U and U.S. Pat. No. 3,297,162 A, it is known to equip a filter, such as a lubricant oil filter of an internal combustion engine, with two separate bypass valves having different opening pressure, each having two operating positions, namely closed or open. In this way, it is achieved that the filter can assume three functional states, namely a fine filtering function, with flow through a fine-pored filter element with two closed bypass valves, a coarse filtering function with flow through a coarse-pored filter element, bypassing the fine-pored filter element with open first bypass valve, and an unfiltered pass-through function, bypassing both filter elements, with second bypass valve also still open.
Here it is regarded as a disadvantage that the technical outlay resulting from the two separate bypass valves is relatively high, resulting in correspondingly high production and installation costs and an increased space requirement.